Reitmeier et al., in U.S. patent application Ser. No. 576,915 filed Feb. 3, 1984 now U.S. Pat. No. 4,622,577, describe a television signal transmission format in which a wide-screen image is conveyed by an "NTSC-like" composite video signal. The line-rate, field-rate and color subcarrier frequency all conform to NTSC transmission standards but the "active" portion of each scan line represents a wide screen image, that is, an image having an aspect ratio greater than the aspect ratio (4:3) of conventional television receiver displays. In an embodiment of their invention the transmitted picture has an aspect ratio of 5:3. If such a signal were to be displayed on a conventional television receiver having a 4:3 aspect ratio kinescope, the image would appear to be compressed horizontally. To avoid such distortion, Reitmeier et al. describe a decoder which provides aspect ratio reduction from 5:3 to 4:3 by cropping the edges of the wide screen image. This is done by sampling the center portion of each line of the wide screen signal that corresponds to a 4:3 aspect ratio picture and time expanding the center samples so as to fill the entire active scan interval of each line.
It is recognized by Reitmeier et al. that expanding the center samples of each line to accomplish aspect ratio reduction will reduce the color subcarrier frequency of the composite wide screen signal in proportion to the amount of time expansion. Specifically, if the aspect ratio is changed from 5:3 to 4:3, then the color subcarrier of the composite signal will be reduced in proportion to the aspect ratio of the expanded signal divided by the aspect ratio of the original signal which, in this case, corresponds to a reduction of 20 percent.
Reitmeier recognized that the reduction in the color subcarrier frequency of the expanded 4:3 aspect ratio composite video signal precluded direct demodulation of the expanded signal using the color burst component of the wide screen signal. To solve this problem the luminance and chrominance components of the expanded signal are separated and the chrominance components are demodulated to baseband using a demodulation carrier wave of reduced frequency derived from the color burst component of the wide screen input signal by means of a phase lock loop (PLL) circuit. The baseband components are then matrixed to generate RGB components for display on a standard (4:3 aspect ratio) kinescope.